In recent years, the aging population increases. Hence, the medical sensing technology becomes more important for early discovery of any physical disorder or illness and a proper treatment thereof. The so-called biosensor refers to an analytical apparatus in which biomolecules (such as enzyme, antibody, etc.) react with a target (such as glucose, potassium ions, cholesterol, DNA, tumor markers, etc.) in a system, and the reaction result is converted to an electronic, optical, thermal, magnetic or wave signal. The major components of a biosensor include a biosensing material, a transducer and an electronic device. A biosensor employs a highly selective biosensing material to react with the target (analyte), transmits the reaction results in a form of an optical, electrical, thermal, magnetic, or wave signal via a transducer, and displays the results with the associated electronics or data processors. Typically, biosensors are divided into enzymatic sensors, immuno sensors, and chemical receptor sensors, etc., based upon the sensitive biological material used. For example, a specific enzyme is used to catalyze the reaction of the targeted analyte, and the corresponding response is properly transformed with a transducer and displayed on the reader device in the system of enzymatic sensor. The structure of a biosensor is more compact than conventional analytic instruments and is easily portable and is more friendly to use. Hence, patients or any users, whenever it is necessary, may use the simple detection method at home to monitor the instant status of a physical condition.
Most of commercially available biosensors employ electrochemical sensing mode for its simple operation, high sensitivity, and reasonable cost. Enzymatic sensor, in which oxidases and dehydrogenases are frequently employed, is one of the most commonly used electrochemical biosensors. Hydrogen peroxide (H2O2) and reduced β-nicotinamide adenine dinucleotide (NADH) are the common co-products of reactions catalyzed by oxidases and dehydrogenases respectively. Consequently, the levels of H2O2 and NADH are often measured to indicate the level of analytes. Therefore, sensors with high sensitivity to H2O2 or NADH imply a great opportunity for biosensors with oxidases or dehydrogenases, respectively.